The present invention relates to a doppler detector for detecting the speed and other information of a moving body by using a microwave signal, and more particularly, relates to such a device for the detection of the speed and the moving direction of a moving body.
The applicable field of the present invention is, for instance, the measurement of the speed and the direction of a car for traffic control purposes. The present invention can be in general utilized for measuring the speed and the direction of a moving body at up to several kilometers or more from the present apparatus.
It has been known that the speed, direction, distance and other qualities of a moving body can be measured by emanating microwave signals to the moving body and receiving the reflected waves from the moving body. The frequency of the reflected wave is changed from the original one due to the well known doppler effect.
If it is desired to detect only the speed of a moving body by using microwave and doppler effect, such detection can be carried out by a simple means comprising a single mixing diode disposed within a waveguide and a low pass filter for treating the signal from the mixing diode. However, in the case of detecting both the speed and the direction of a moving body, a complicated apparatus like the Japanese patent publication No. 16905/62 (after examination) must be utilized. According to the Japanese patent publication No. 16905/62, the signal from an oscillator is divided into two signals, transmitting wave toward antenna and reference wave for mixing, by using a magic T. The reference wave for mixing is then brought to two waveguides with a phase difference of .phi. through a phase generator, and then applied to mixing diodes disposed in the waveguides, respectively. On the other hand, the signal emanated from the antenna collides with the moving body and the reflected wave returns to the same antenna, so as to be brought to said two waveguides with the mixing diodes at the same phase angle for application to the mixing diodes, respectively. At the mixing diodes, the reference waves for mixing and the reflected wave are received and are mixed. Since the reference waves for mixing at the two diodes have the aforesaid phase difference .phi., the output signals from those mixing diodes have a phase difference .phi.. The detection of the moving direction is carried out by checking whether the mutual phase difference between the output signals from the mixing diodes is +.phi. or -.phi..
However, the prior doppler device for measuring both the speed and the direction must use, in combination, a wide variety of microwave devices, including a magic T, a phase generator, the waveguide for dividing the signal, et al. As a result, the conventional doppler device has shortcoming in that the device is costly due to the complicated largescale structure.